In telephone or telephone-like communications systems, system tones and ringing are used to inform a system user of the status or progress of a call to which the user is either an actual or an intended party. System tones include dial tone, busy tone, reorder tone, ringing feedback tone, and various prompting tones. Because a switching system is typically a source of these tones, the switching system includes an arrangement for generating these tones and an arrangement for distributing the tones to users' telephone lines. In alternative implementations, such as ISDN, the tones are generated locally at users' terminals in response to messages received by those terminals from the switching system.
Many switching system owners (e.g., private-party owners of PBXs, public-network owners of central office switches) would like to customize tone behavior for numbers in their network numbering plans. However, the way tones are presently handled by switching systems is to hard-code the tone treatment into the call-processing software, such that tones are given only in places where the designer of the switching system believes that tones should be given based on the designer's fixed network-number constructs. Deleting or adding tones, administratively by the customer in places where the customers would like to have them, is typically impossible, because the switching system cannot intelligently handle network-number constructs that do not conform to the structure that was implemented by the system's designer.
In a complex network (e.g., the international direct-dialed network), dialed network numbers can often be quite long. The longer the dialed network number is, the more likely it is that the user will misdial, and hence the more likely it is that network facilities will be needlessly tied up and time will be wasted while the entire number is (mis)dialed and thereafter redialed.